Re: [Qemu-devel] MTTCG External Halt

[Peter Maydell]

On 31 January 2018 at 18:51, Alistair Francis <address@hidden> wrote:
> On Wed, Jan 31, 2018 at 10:48 AM, Peter Maydell
> <address@hidden> wrote:
>> On 31 January 2018 at 18:17, Alistair Francis <address@hidden> wrote:
>>> On Wed, Jan 31, 2018 at 9:13 AM, Paolo Bonzini <address@hidden> wrote:
>>>> cpu->halted = false likewise should not be needed here, but you cannot
>>>> just clear CPU_INTERRUPT_HALT either.  You need to set a *different*
>>>> interrupt request bit (the dummy CPU_INTERRUPT_EXITTB will do) and
>>>> cpu_handle_halt will clear cpu->halted.
>>>
>>> The problem with that is that I hit this assert for ARM CPUs:
>>>
>>> qemu-system-aarch64: ./target/arm/cpu.h:1446: arm_el_is_aa64:
>>> Assertion `el >= 1 && el <= 3' failed.
>>
>> Backtrace from when you hit that might be useful...
>
> Here it is:
>
> (gdb) bt
> #0  0x00007ffff1a030bb in __GI_raise (address@hidden) at
> ../sysdeps/unix/sysv/linux/raise.c:51
> #1  0x00007ffff1a04f5d in __GI_abort () at abort.c:90
> #2  0x00007ffff19faf17 in __assert_fail_base (fmt=<optimized out>,
> address@hidden "el >= 1 && el <= 3",
> address@hidden
> "/scratch/alistai/master-qemu/target/arm/cpu.h", address@hidden,
> address@hidden <__PRETTY_FUNCTION__.24916>
> "arm_el_is_aa64") at assert.c:92
> #3  0x00007ffff19fafc2 in __GI___assert_fail
> (address@hidden "el >= 1 && el <= 3",
> address@hidden
> "/scratch/alistai/master-qemu/target/arm/cpu.h", address@hidden,
> address@hidden <__PRETTY_FUNCTION__.24916>
> "arm_el_is_aa64") at assert.c:101
> #4  0x00005555557eb872 in arm_el_is_aa64 (el=0, env=0x55555723c7f8) at
> /scratch/alistai/master-qemu/target/arm/cpu.h:1446
> #5  0x0000555555951233 in arm_el_is_aa64 (el=0, env=0x55555723c7f8) at
> /scratch/alistai/master-qemu/target/arm/cpu.h:1838
> #6  0x0000555555951233 in arm_cpu_do_interrupt (cs=0x555557234550) at
> /scratch/alistai/master-qemu/target/arm/helper.c:8020

The problem is here (or further down the callstack) -- you
definitely don't want to be trying to take an interrupt from
the guest's perspective, which is what arm_cpu_do_interrupt()
is for...

This is probably happening because cpu->exception_index isn't
right at this point (though the arm code has a habit of leaving
it set to whatever its value was last...)

> #7  0x000055555585e75b in cpu_handle_exception (ret=<synthetic
> pointer>, cpu=0x555556c64200)
>     at /scratch/alistai/master-qemu/accel/tcg/cpu-exec.c:532
> #8  0x000055555585e75b in cpu_exec (address@hidden) at
> /scratch/alistai/master-qemu/accel/tcg/cpu-exec.c:748
> #9  0x000055555582d963 in tcg_cpu_exec (cpu=0x555557234550) at
> /scratch/alistai/master-qemu/cpus.c:1297
> #10 0x000055555582d963 in qemu_tcg_cpu_thread_fn (arg=0x555557234550)
> at /scratch/alistai/master-qemu/cpus.c:1502
> #11 0x00007ffff1db37fc in start_thread (arg=0x7ffef6b43700) at
> pthread_create.c:465
> #12 0x00007ffff1ae0b5f in clone () at
> ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

thanks
-- PMM